Mechanical printing of daylight fluorescent compositions



United States Patent flice 2,845,023 Patented July 29, 1958 MECHANICALPRINTING F DAYLIGHT FLUORESCENT COlVIPOSITIONS Joseph L. Switzer,Cleveland Heights, and Robert C. Switzer, South Euclid, Ohio, assignorsto Switzer Brothers, Inc., Cleveland, Ohio, a corporation of Ohio NoDrawing. Application February 21, 1950 Serial No. 145,592

14 Claims. (Cl. 101-426) This invention relates to an improvement in theart of producing daylight fluorescent products and, more particularly,to the mechanical printing of daylight fluorescent coating compositions.This application is a continuation-in-part of our copending applicationfor Fluorescent Compositions, Serial No. 414,285, filed October 9, 1942,and for Daylight Fluorescent Pigment Compositions, Serial No. 575,364,filed January 30, 1945, and Serial No. 57,932, for Daylight FluorescentDisplays, filed November 2, 1948. Application Serial No. 575,364 issuedas U. S. Patent No. 2,498,592 on February 21, 1950 and ApplicationSerial No. 57,932 was abandoned in favor of said patent.

One important desideratum in producing visually striking color contrastsis the obtaining of colors of maximum brightness in delineated areaswhich can contrast sharply with adjacent areas. Brighter colorsobviously reflect more light to the eye than duller colors, and, thoughthe eye distinguishes by contrast, as a general rule the more lightdelineated areas of a display direct toward the eye, the more effectivethe display is. In producing printed displays and display products to beviewed in visible light, the art has heretofore been limited to inkscontaining dyes and/or pigments having subtractive colors, that is, dyesand/ or pigments which exhibit color due to the phenomenon known asselective reflection and absorption. The irremedial fault of suchsubtractive colors, from the point of view of one desiring maximumbrightness in a display, is that the subtractive colors cannot reflectmore than a fraction of the visible light incident upon thesubtractively colored area of the display. For example, a blue pigmentwhich reflected as much as a half of the blue in incident white lightwas regarded as a good bright blue pigment. And since the blue lightreflected by such a pigment would be but a minor percentage of the totalamount of incident visible white light, the subtractive colors of priorprinting inks make very ineflicient use of the energy in incident whitelight.

In the above identified U. S. Patent No. 2,498,592, we have disclosedcoating compositions which are capable of exhibiting color due to thephenomenon best described as daylight fluorescence, the term daylightbeing used to describe natural sunlight and artificial polychromaticlight generally referred to as white light and usually containing someultraviolet. Such daylight fluorescent coating compositions may be soexceptionally bright that their colors, in contrast with ordinarysubtractively colored compositions, appear to be different in kindrather than exhibiting an exceptional difference in degrees ofbrightness. The reason that such daylight fluorescent coatingcompositions may be so bright is that they contain fluorescent agents,termed fluoragents, which not only exhibit color due to the phenomenonof selective reflection and absorption but also fluoresce in response tolight which would be dissipated as heat by subtractive colors. Thus, reddaylight fluorescent coating compositions may project (i. e. emit andreflect) over one hundred and twenty percent of the light of the samehue which is present in the incident daylight.

Unfortunately, when daylight fluorescent inks are applied byconventional mechanical printing methods, such as typographic, intaglioor planographic methods in which the sheet or web to be printed is givenan impress from the inked plate and then dried, the daylight fluorescentinks do not exhibit the maximum daylight fluorescence of which they arecapable, but rather are extremely pale and exhibit little daylightfluorescence.

If a subtractively colored ink lacks suflicient tinctorial strength, theusual practice in the printing art is to increase the proportion ofcoloring agent in the printing ink. If one follows this teaching of theprior art by increasing the proportion of fluoragent in our daylightfluorescent printing inks, an ink having increased tinctorial strengthmay be obtained but the daylight fiuorescence of the ink will bedestroyed, for reasons explained at length in our above identified U. S.Patent No. 2,498,592. Even daylight fluorescent printing inks having themaximum permissible proportion of fluoragent to vehicle will still betoo pale to exhibit effective daylight fluorescence when printed bycustomary printing techniques. In order to obtain a coating of daylightfluorescent printing ink which will have the optimum amount offluorescent dye per unit of area of surface covered and not exceed themaximum permissible proportion of fluoragent to volume of printing inkvehicle, as disclosed in our above disclosed copending U. S. Patent No.2,498,592, the thickness of ink deposit required to produce effectivedaylight fluorescence exceeds that which can be applied by an impressaccording to conventional mechanical printing processes employingprinting plates and inking mechanisms heretofore designed to printconventional subtractive colored printing inks. Such printed thicknessesor deposits as are required for satisfactory daylight fluorescence haveheretofore been obtained by stenciling processes, such as the silkscreen process, for example. The disadvantages of such stencilingprocesses, however, are that the processes are slow; the thick depositsof ink are slow to dry, with the result that slipsheeting or racking ofindividual printed sheets is required; precise, accurate delineation isdiflicult to obtain; and if more than one color is to be printed,additional color can be printed only after allowing the preceding colorto dry, with the result that registry is diflicult to obtain.

We have, however, solved the above problems involved in daylightfluorescent printing and it is, accordingly, the object of thisinvention to provide a method for mechanically printing daylightfluorescent inks from mechanical plates. Advantages of this inventionare that high speed, accurately delineated daylight fluorescent printingis obtained, instantaneous drying without slip-sheeting or racking isobtained, and a plurality of colors may be printed in one pass throughthe printing press, thus minimizing registry problems.

Other objects and advantages of this invention will be apparent from thefollowing specification and claims.

As pointed out in our above identified U. S. Patent No. 2,498,592,optimum daylight fluorescence is obtained in coatings containing fromapproximately .00006 to .00003 gram of daylight fluorescing dye persquare centimeter of surface covered at concentrations of less than .01gram of dye per cubic centimeter of coating. The printed thickness of adry daylight fluorescent film should vary from at least .001 to .002inch and, when using a preferable concentration of fluoragent ofsomewhat less than .01 gram per cubic centimeter of coating, a minimumthickness of .003 inch may be required. Since the volatile solvent in aprinting ink may run from about twenty to as high as forty percent byvolume, this means that a mechanical printing plate would be required todeposit in one pass a thickness of printing ink varying fromapproximately 1 to as many as 5 mils. Printing plates depositingwsuchthicknesses of conventional ink would obviously gum up and smear.

The type of..plate generallyable to carry successfully the greatestthickness of ink: is theintaglio or gravure type ofplate. Such platesarefrequently used to deposit con ventional. inks, particularly theso-called. transparent lacquerinks, in:thicknesses as great as .5 mil.There are available on thezmarketgravure presses designed forrnulticolorwork in which as many as seven gravure rollers may beemployed to depositdifferently colored inks on the web-.being printedrThere are also available on the market printing inksolvents such asButyl Cellosolve (ethyleneglycol monobutylether), Butyl Carbitol(diethylglycol:ethylether), the so-called low boiling narrow cuts ofpetroleum, and thelike, which have a low vapor pressure at ordinaryroom: temperature and high vapor pressure at temperatures moderatelyelevated above room temperature. Thus, by-the application of heat, thesesolvents permittheso-called flash-drying of printing inks immediatelyafter application to the web. In general, we have found that the problemmay be solved by modi tying the multicolor gravure presses by providingthe presses with successive duplicate intaglio rolls, each printing thesame ink. on the same areas of the web. This is in contradistinction tothe usual practice on such multicolor presses of employing successiveintaglio rolls which print different colors and/or diflerent areas ofthe web. By employingprinting inks having the proper proportion ofdaylight fluorescent fluoragent and flash-drying solvents, and thenover-printing the same area with the same daylight fluorescent ink in ahigh-speed multicolor gravure press as described above, accuratelydelineated areas may be printed rapidly. The printed areas will have thedesired: daylight fluorescence, due to the fact that each daylightfluorescent area-will have a plurality of thin coatsof daylightfluorescent ink separately applied but fused together. The flash dryingsolvents will permit a layer of daylight fluorescent ink to be printedsubstantially immediately and in exact register, upon a precedingprinted layer of daylight fluorescent ink without smearing or piling up;this result is due to the fact that the preceding layer of inkissubstantially dry by the time the successive layer is applied. Thus, forexample, if three successive layers of daylight fluorescent inks,containingabout 33% solvent, are successively applied in the same area,each layer being initially about" .5 mil thick, then allowing forevaporation of solvent, a final printed area will be obtained having adaylight fluorescent coating approximately one mil thick. It should thusbe apparent that if .4 or .5 mil is thegreatest ink thickness which canbe deposited by a gravure roll, at least three successive duplicate and.registered gravure impressions'should be made to obtain a satisfactorydaylight fluorescentprinting. To expedite flash-drying, suitable meansto heat the volatile solvent between successive impresses are preferablyemployed; such heating means may be open. or radiant gas flames,infra-red lamps, or ultra high-frequency induction heating apparatus,although such heating means may be omitted between the first and secondimpresses if the printing is on a web having ,suflicient absorptiveproperties for the ink solvent.

It should also be pointed out that the foregoing requirement for aminimum thickness of a daylight fluorescent coating requires a diffusereflecting under'surface on which the coating is applied. Since mostwebs to be printed are white, the web itself usually provides thenecessary diffuse reflecting under-surface. Where the web is not whiteor is not of the same color as the daylight fluorescent ink, suitablesteps should be taken to provide a proper under-coat.

4%? Illustative but not limitative examples of applications of thisinvention are as follows:

Example 1 A red daylight fluorescent printing ink is prepared from adaylight fluorescent pigment composed of a dye and a solvating carrieras disclosed in Example 5 of our U. S. Patent No. 2,498,592, a.transparent resinous vehicle to bind the pigment, and a flash dryingsolvent, such as Butyl cellosolve, in suflicient quantity to impart thedesired fluidity to the-ink; so that in the'ink the amount of solventwill be approximately 20% by volume and the proportion of the daylightfluorescent dye will be approximately .004 gram per cubic centimeter ofthe solids content of the solvating carrier. The ink is printed by meansof a seven-color gravure press upon white poster paper havingapproximately reflectance compared to a standard magnesia block. Eachroll in the press applies an ink deposit approximately .5 mil thick, allsucceeding deposits being in exact register with the first deposit andinfra-red. rays being used to flash-dry the ink between successivestages. The resultant deposit of a plurality of thin, dried, fusedlayers, being approximately 2.8 mils thick, contains very close to.00003 gram of meta diethylamino phenolphthalene hydrochloride persquare centimeter of surface covered.

If desired delineated areas of other sheets are printed so that aconventional twenty-four sheet billboard poster will be provided tocarry a design printed in the red daylight fluorescent ink. Since it isprefearble to employ the daylight fluorescent ink in large masses toobtain the maximum effect, some ofthe sheetsof the billboard poster maybe entirely covered with daylight fluorescent ink, and others may becovered in only limited areas. If thebalance of the poster is printedindark subtractive colors, the contrastratio between: the daylightfluorescent indicia andthe' non-fluorescent background may be many timeshigher than the contrast ratio obtainable if the indicia had beenprinted innondaylight fluorescent colors. When viewed under manylighting conditions, the areas printed in daylight fluorescent colorsappear to be artificiallyilluminated due to the fact that the daylightfluorescent indicia are actually emitting light as well asreflectingpart of the incident white light; color photographs ofsignshaving daylight fluorescent indicia and bordered withlighted neontubes reveal that, under certain lighting conditions, i. e. at dawn,dusk, or in shadow, the daylight fluorescent indicia are actuallybrighter-than the adjacent lighted neon tubing.

Example 2- An ink similar .to that employed in Example 1 is prepared,except that the pigment employed contains approximately .01 gram ofdaylight fiuorescing dye per cubic centimeter of solvating carrier; Theink is deposited in register from the first three rolls of a multicolorgravure press on a white sulfite-surfaced carton Example 3 A carton isproduced similarly to that disclosed in Example 2, except that a seconddaylight fluorescent ink, similar to that employed inExample 1 but forthe different color of the fluoragent, is printed in areas adjacent toareas printed in Example 1. If a seven roll gravure press is employed, aseconddaylight fluorescent color may be printed by the three rolls whichsucceed the first three rolls.

The final roll may be employed to print an ordinary subtractive color toborder, shade, or otherwise complement the daylight fluorescent printedareas.

Example 4 A daylight fluorescing ink is prepared by dissolving acellulose ester, such as cellulose acetate in the flash drying solvent,the proportion of solvent to solids conan under-coat of white opaque inkon the web at the areas to'be covered by the daylight fluorescentdesign: subsequently deposits of the daylight fluorescent ink are thenprinted in register with the white under-coat, until the desired depthof deposit of daylight fluorescent ink is obtained, to provide adaylight fluorescent design on white-printed surface of the transparentweb.

Example 5 A transparent web is printed in the manner disclosed inExample 4, except that the deposits of daylight fluorescent ink areprinted directly on the web and a final over-coat of white opaque ink isprinted on the daylight fluorescent deposit. The daylight fluorescentdesign is then viewed from the opposite side through the web.

Example 6 Example 7 A web of transparent film is printed as in Example'5, except that the final white over-coat is omitted. Instead, the filmis laminated to a glazed white paper. This laminated product may be usedas cover stock for advertising pamphlets, books and the like.

The deposition of delineated areas of daylight fluorescent inks by thepreceding examples has the advantages of permitting the use ofsubstantially conventional printing machinery and inks which behave insubstantially the same manner as conventional subtractive colored inks.The outstanding disadvantages of the preceding examples is that multipleimpresses are required and, due to the loss of solvent in each repeatedimpress, the mileage of the daylight fluorescent inks, in terms ofsquare feetof printed area per gallon of ink, is poor. While the mileageof daylight fluorescent inks will seldom approach that of conventionalsubtractive color inks due to the thickness of deposit required for highchroma and purity of color (relative lack of pastelness) in daylightfluorescent colors, we havefound several alternative types of noveldaylight fluorescent printing compositions and methods of printing themwhich substantially eliminate the solvent loss of the preceding examplesand minimize the repetitive impresses, permitting the printing ofdaylight fluorescent areas with one impress in most instances. Theelimination of excessive solvent loss and repetitive impresses asobtained with the following alternative procedures and compositions isoffset by the fact that usually special attachments to conventionalprinting equipment is required. Whether the procedures set forth in thepreceding examples or in any one of the alternative procedures set forthbelow will be more economical and, therefore, preferable, will dependupon factors pertinent to each given situation.

A general characteristic of the several alternative procedures andprinting compositions is that printing is accomplished While thedaylight fluorescent printing composition is in a relatively semi-fluidand tacky condition and solidifies without an appreciable loss ofvolume.

Since it is possible to obtain good daylight fluorescence with printedfilms having an approximate minimum thickness. of 1 mil and since thefollowing alternative daylight fluorescent printing compositions andprocesses Will often permit the deposition of films as thick or thickerthan 1 mil, single impress printing of daylight fluorescent inks isthereby frequently obtainable. Even if multiple impresses are necessary,the number of impresses which would be required according to thepreceding examples are reduced and the solvent losses are eliminated orgreatly minimized.

In such single or minimum impress printing, intaglio plates aregenerally preferred, since the depth of daylight fluorescent printingcomposition deposited may be precisely controlled by the depth of etchin the plate and the plates may frequently be more deeply etched thanwhen used for printing conventional solvent-type inks. Typographicplates may be employed, but generally impose the problem of controllingthe viscosity of the print ing composition and the thickness thereof onthe inking rolls so that the desired thickness of composition will bepicked up on the raised surface of the plate and deposited on the web tobe printed with insuflicient pressure to squeeze out the relativelyfluid composition from between the type face and the web to be printed.

Planographic ofiset printing may also be accomplished by printing thedaylight fluorescent composition in the required thickness on thetransfer web or blanket and then offsetting onto the web to be printedafter the daylight fluorescent .composition has set or hardenedsufiiciently to withstand the offsetting pressure. One very simple typeof offset printing is practiced by printing daylight fluorescent indiciain the desired thickness upon glassine or wax-coated films and thenafter the indicia has hardened, offsetting the indicia onto the web tobe printed by means of a heated iron or platen applied to the back ofthe transfer web (nearly all daylight fluorescent printing compositionsare thermo-adhesive or may be rendered so by means of an over-print ofthermoadhesive material).

A relatively simple procedure and composition for single impressdaylight fluorescent printing comprises the application to themechanical printing plate of a molten printing composition comprised ofa normally solid thermo-plastic vehicle and a daylight fluorescent dyeand/ or pigment dispersed therein. With the molten composition depositedin or on the mechanical plate in the desired thickness, the daylightfluorescent composition is transferred from the plate to the web to beprinted while the composition is in a tacky condition. By cooling thecomposition on the web, the printed composition is solidified in thedesired thickness to produce daylight fluorescent indicia.

To obtain a normally tack-free print, the vehicles for the abovegenerally described. hot-melt printing compositions preferably have afreezing point in excess of approximately C. To avoid injury to thedaylight fluorescent dyes and/or pigments and the web to be printed uponand also to avoid excessive equipment costs, the hot-melt vehicle willpreferably have a printable viscosity below 250 C. The preferredhot-melt vehicles have a narrow freezing point range only slightly abovethe minimum freezing point permissible to maintain tackfree printing atambient temperatures likely to be encountered during} subsequent use orconversion of the printed-web. Such preferred vehicles permit, on theone hand, the use'of-lowertemperatures to maintain printable-fluidityandthereb'y permit theuseof daylight fluorescent dyes which might be'injured at highertemp era tures and, on the other hand, permittheink tobe set almost immediately on theweb, thereby allowing'higher speedprinting.

In carrying outthe above outlined hot-melt printingofdaylightfluorescentcompositions; the ink reservoirs, doctor blades,inkingrolls, and like equipment are heated, usually electrically, to atemperature slightly in excess of the melting point'range of thedaylight fluorescent composition. The web to be printed is usually atroom temperatures (ZS-30C.) but may be chilled to a lower temperaturebefore or immediately after'contact with the printing plate in orderto-shorten the time for setting the ink. The runningtemperature of themechanical printing plate is usually at thefreezing point range of theprinting composition, although, depending upon the characteristics ofthe printing composition, in some instances release of the compositionfrom the plate to' the web isimproved by heating the plate above themelting range of the composition and, in other instances, release fromthe plate and speed of setting are improved by chilling the plate.

Illustrative but not limitative examples of satisfactory hot-meltdaylight fluorescent printing compositions are set forth in thefollowing Examples 8 to 11, in which the daylight fluorescent pigmentmay be any one of those described in our'above mentioned U. S; PatentNo. 2,498,592.

Example8 Parts by Weight Daylight fluorescent pigment; 50 Ethylcellulose Beeswax (white) 45 (Printable'at 80 C.)

Example 9 Parts by weight Daylight fluorescent pigment l2 Ethylcellulose l Beeswax (white) 9 Varnish 00 (boiled linseed oil) 2(Printable at 85 C.)

Example 10 Parts by Weight Daylight fluorescent pigment 5O n-butylmethacrylate 5 Beeswax (white) (Printable at 85 C.)

Example 11 Parts by weight Daylight fluorescent pigment n-butylmethacrylate l0 Beeswax (white) 40 (Printable at 100 C.)

In the foregoing examples, the freezing temperature range may bedecreased or increased by decreasing or increasing the proportion ofethyl cellulose or butyl methacrylate with respect to the beeswax in theresin-wax vehicle for the daylight fluorescent pigment. Vehiclescomprised essentially of resin-wax mixtures, mixtures of resins,mixtures of waxes, or like mixtures of thermoplastic ingredients,generally provide the most satisfactory results although, usually lesssatisfactorily, a vehicle containing a single thermoplastic ingredientmay be employed. In place of the beeswax, othermicrocrystalline waxymaterials may be employed, such as animal, vegetable, or mineral waxes(preferably modified with naturally-occurring or addedcrystalization-inhibiting petroleum or like resins), high melting-pointalcohols and esters, hydrogenated oils andzoil acids, and high-meltingsoaps may be employed.

In-place-of thecelluloseether'and alkyl acrylicacidresins shown in theexamples, other relatively highrneltingthermoplastic resins-maylie-employed," such ascellulosresters,-modified and unmodified alkyds,polyvinyl and vinyl idene resins, natural-and synthetic petroleum 'andhydrocarbon resins, such as polyethylene, and the like may be employed.Flexibility may be imparted to the resins and compatible resin=waxmixtures by suitable plasticizers, and where ultimate tack-'freecharacteristics are essential,

air or heat 'hardened'additives'may be employed; such as the linseed oilvarnish employed in Example 9 or lowtemperatureandpressure'thermosetting resins'of =the allyl ester type.

In addition to th'e"hot-melttype of solvent-less ink; anothersatisfactory relativelysolvent-less daylight fluorescent ink havingan'insignificant"loss' of. volume when set on the printed web isione inwhich the vehicle is.essentia1- 1y a plastisol, i. e., a' relativelyfiuidcdispersion ofa suitable elastomeric resin in a non-volatileplasticizer therefor, the plastisolbeing characterizedby the ability tokick-over to a stable 'flexible gel of resinand plasticizer when raisedto.an elevated temperature. To print such a plastisol daylightfluorescent composition, the composition, thinnedto the desiredviscosity if necessary,,is

printed on the Web in the desired thickness andis then heated tokick-over the plastisol 'vehicle and set the daylight fluorescentprintingcomposition. The plastisolcompositions. are. particularly.satisfactory where the printed. webis likely to.besubjectedtoconsiderable flexing, as in. wrapping and.bag,machines, forexample. Due to. the relatively poor. adhesiveness of the elastomericresinsato dissimilar. films, .they are preferably printed on fibrouswebson which the gels will interlock with the surface fibers or on webshaving a resinous surfacecoating to which.- the gelsare adhesive. Thepreferable surface upon which the daylight fluorescent. compositionsare:

printed. should also. retain the desired whiteness when wetted withtheplasticizer.and. notfbedarkenedor renderedi translucent by, the tendencyof the; plasticizers to migrate fromthegels.

The-following are examples of suitable printable day.- lightfiuorescent-plastisol compositionsin which the day: lightfluorescentpigmentmaybe any one'ofthe pigments.- disclosed in ourxU. S.PatentNo. 2,498,592.

Example. 12:

Parts by weight Daylight fluorescent-pigment 45 Powdered polyvinylchloride; 23 Di-octyl-phthalate 27 Naphtha (paraflinic) 5 Example 13Parts by weight Daylightfluorescentpigment 50 Powdered vinylchloride-vinyl acetate copolymer (20% vinylacetate) 25 Di-octylphthalate. 20 Di-butylphthalate 5 The elastomeric resin and pigment aresuccessively ground into the plasticizer, as in Example 12. The.resultant paste is printed and the printed web is heated to C. and thencooled.

Example 14 stillanother relatively solvent-less daylight fiuores-'.pastel shades and daylight fluorescent tints. cificallywith respect toknown daylight fluorescent dyes hicle comprising a solution of ananhydrous hygroscopic,

solvent for a resin which is insoluble in aqueous solutions of thesolvent. An exampleof such a vehicle is a solution of ethylene glycol inpolyvinyl formal or a like acetal of polyvinyl alcohol. After printingthe resultant paste on a fibrous Web, the web is subjected to dry steamjets. As the steam is absorbed by the glycol, the resin is deposited onthe web from the aqueous-glycol solution which, in turn is absorbed inthe web and/ or volatilized off by the heat of the dry steam.

In all of the foregoing examples, the vehicle for the daylightfluorescent pigment or the solvated daylight fluorescent dye issubstantially transparent to both visible and near ultraviolet light. Itis also to be noted that in all of the examples employing a daylightfluorescent pigment (made according to our U. S. Patent No. 2,498,- 592and containing approximately 1% of solvated daylight fluorescent dye)the proportions of vehicle to pigment in the resultant printed ink areapproximately equal. In such proportions, daylight fluorescent indiciaof full chroma and purity will be obtained when the thickness of theseprinted daylight fluorescent compositions is from 1.25 to approximately2 mils, an optimum thickness being approximately 1.5 mils. As pointedout in said patent, there is not only an upper limit to theconcentration of daylight fluorescent dye in its solvating carrier butalso an optimum and an upper limit to the number of molecules of dye perunit of area. If any one of these upper limits are exceeded, either asto the concentration of dye in the solvating carrier or as to the numberof solvated dye molecules per unit of area, the daylight fluorescence ofthe dye will be destroyed. With these general principles in mind, it isobvious that, for any given concentration of solvated dye less than theupper limit of concentration permitting daylight fluorescence, (a) thereis an upper limit to the thickness of composition which may be printedif it is to retain daylight fluorescence; (b) there is an optimumthickness for the printed composition; and (c) there is a practicalminimum thickness if daylight fluorescence of full chroma and purity ofcolor is to be obtained, but no minimum thickness for Stated spetheproportions are as follows:

.0005 gram of solvated dye per square centimeter of dry ink is apractical maximum in any daylight fluorescent system composed of asingle dye and a solvating material.

.00006 to .00003 gram of daylight fluorescent dye per square centimeterof surface covered [and at concentrations of less than .01 gram percubic centimeter of ink] will produce optimum daylight fluorescence.

.000015 gram of daylight fluorescing dye per square centimeter is theminimum amount of dye which will exhibit daylight color, although forpurposes of tints, no practical minimum has been found, since daylightfluorescent tinting eflects have been noted in dilutions exceeding onepart of daylight fluorescing dye in many.

million parts of solvating material.

While further study of the phenomenon of daylight fluorescent dyes andpigments indicates the above proportions may have to be translated fromterms of grams of dye to terms of the number of chromophoric group andfluorophoric groups capable of responding to incident visible as well asultraviolet light if and when all such groups can be identified, it isalso apparent that if any new daylight fluorescent dyes and pigments arefound not to answer to the above specifically stated maxima, optima, andpractical minimum, the variations therefrom will be proportional.

As indicated by Example 4, it is not necessary that daylight fluorescentpigments comprising a solvated daylight fluorescent dye and a resinouscarrier be employed as the only fluoragent in theprinting compositions.In-- stead, the printable composition may be unpigmented'and carry thedaylight fluorescent dye solvated in the nonvolatile vehicle. Or thecompositions may comprise a daylight fluorescent pigment and a vehiclein which a daylight fluorescent dye will remain solvated in less thanthe maximum permissible concentration. It is generally less desirable tosolvate the dye in the'vehicle. since the dyes are seldom as stable aswhen solvated in a resin pigment and may tend to becomeover-concentrated at the surface of the printed compositions. Solvationof the dye in the printed vehicle, however, usually permits the use ofthinner printed thicknesses and, where the vehicle is also pigmented,the instability and possible over-concentration of the dye solvated inthe vehicle is usually less apparent than when no pigments are employed.

Regardless of whether the fluoragent is carried into the finishedprinted indicia in the form of a pigment, a dye solvated in the vehicle,or both, and whether or not the relatively fluid printing composition isprinted by a single impress or by multiple impresses, application of theprinciples of this invention reveal that, in the final printed indicia,the fluoragent must never be concentrated in the resultant solidifiedcomponent of the printing composition in a concentration in excess ofthe maximum permissible for daylight fluorescence of that fluoragentand, of course, the fluoragent must be dispersed in a daylightfluorescent state in said component. Further, assuming uniform thicknessof deposit in a given delineated area, the maximum thickness of daylightfluorescent printing composition which can be deposited may be computedaccording to the formula:

where T is the maximum thickness of composition to be printed, M is themaximum amountof the fluoragent (per' unit of area) permitting daylightfluorescence, p is the proportion of the volume of solidifiablecomponent, when solidified, in a given volume of the printingcomposition, and c is the concentration of fluoragent in thesolidifiable component of the composition (expressed in terms of amountof fluoragent/unit volume of composition per volume of solidifiablecomponent, when solidified/unit volume of composition). Similarly,

where t is the minimum thickness of the printing composition to beprinted for full chroma of the daylight fluorescent composition, m isthe minimum amount of the fluoragent per unit of area permitting fullchroma of the daylight fluorescent fluoragent, and p and c are informula (a) above. (Note that the volume of the fluoragent must beincluded in the volume of the solidifiable component.)

It is frequently desirable to print thicknesses of the compositionsgiving less than full chroma and purity of the daylight fluorescenthues, notonly for the attractive tints produced, but also, when printedwith subtractive colors in the same delineated areas togive a bloom tothe subtractive colors. Such subtractive colors are pref-. erablytranslucent; particularly. when printed over or simultaneously with thedaylight fluorescent compositions; the bloom produced is usually morepronounced when the hue of the subtractive color is the same or adjacento the hue of the daylight fluorescent color.

Except for the fact that daylight fluorescent printing is not yet asresistant to weathering as non-daylight fluorescent printing, anyprinted device or article intended fective if printed withdaylightfluorescentprinting. Such 1 l signnllingand display devices mayrange from billboards and posters and similar devices for advertisingpurposes to articles'ofwearing apparel and from military maps to fishlures, to give a few examples illustrating the scope of the field inwhich daylight fluorescent printing is useful. The-supporting structuresupon which the daylight fluorescent compositions are printed are usuallysheets and websof fibrous and non-fibrous material such as, paper,fabric, films and like organic materials, but the support ing surfacesare not limited to such materials or strucl tures. For example, mostmetal and glass articles are intended for uses which would extend wellbeyond the life of the printed daylight fluorescent compositions, butwhere weathering or permanence is not a controlling factor, it is'frequently desirable to print daylight fluorescent compositions onstructures and devices of inorganic material, suchas'metal cans andglass jars used for packaging purposes.

In viewof the foregoing modifications and illustrative species of ourinvention, it is apparent that our invention isnot limited to theembodiments disclosed but only by the scope of the following claims.

What is claimed is:

1. The method of printing daylight fluorescent media comprising thesteps of applying to a mechanical printing plate a relatively fluid andtacky daylight fluorescent composition comprised of a dispersed solvateddaylight fluorescent fluoragent'and a vehicle containing a non-volatile,transparent, relatively solidifiable component, the proportion of saidfluoragent. to said solidifiable component not exceeding, the maximumconcentration at which said fluoragent will exhibit daylightfluorescence; depositing, from said plate onto a delineated area of areceiving structure in a substantially uniform thickness, a volume ofsaid composition providing an amount of fluoragent per unit of areabetween the maximum and minimum required to exhibit daylightfluorescence of full chroma and purity of hue; solidifying saidcomponent to a relatively nonetacky condition while retaining thereinsaid fluoragent in a daylight fluorescent state; and removing theportion, if any, of said relatively fluid composition not retained insaid solidified component.

2. The method of printing daylight fluorescent media as defined in.claim 1 in which the vehicle of the composition applied to a mechanicalprinting plate contains a a tially full chroma and purity and in whichthe solidifiable component of each impress prior to the ultimate impressis solidified to a relatively non-tacky condition prior to thesucceeding impress.

4. The method of claim 3 in which the surface of the delineated area ofthe receiving structure diffusely reflects visible light of the hue ofthe daylight fluorescent composition.

5. The method of claim 4 in which the surface of the delineated area ofthe receiving structure is white.

6. The method of claim 3 in which the receiving structure is atransparent film and including the step of superimposing on saidultimate impress a layer havinga surface adjacent said ultimate impresswhich diffusely reflects light of the hue of said daylight fluorescentcomposition.

7. The method of claim 6 in which the surface of said superimposed layeradjacent said ultimate impress is white.

8. The method of claim 3 in which the daylight fluorescent compositioncontains a volatile solvent for at least a portion of thesolidifiablecomponent thereof, said solvent.being characterized by a.relatively low vapor pressure at room temperature which increases to arelatively high vapor pressure at an elevated temperature at a rategreater than the rate of temperature increase and including' the step ofrapidly heating the position of composition deposited by eachpenultimate impress toflash dry the solidifiable component thereof priorto a successive impress.

9. The method of claim 3 in which a portion of the solidifiablecomponent of the daylight fluorescent composition is thermoplastic andis characterized by solidifying above room temperature and including thestep of coooling the fraction thereof deposited by a penultimate impressto its solidification point prior to a successive impress.

10. The method of claim 3 in which the solidifiable component of thedaylight fluorescent composition includes a plastisol comprised of aresin and a nonvolatile plasticizer therefor and including the step ofheating the fraction thereof deposited by a penultimate impress tokick-over the plastisol to relatively stable gel prior to a successiveimpress.

11. The method of claim 3' in which the solidifiable component of thedaylight fluorescent composition includes a solution of a hygroscopicanhydrous solvent and a resin soluble in said anhydrous solvent butinsoluble in aqueous solution thereof and including the step ofsubjecting the fraction thereof deposited by a penultimate impress towater vapor, to deposit the resin on the receiving surface prior to asuccessive impress.

12. The method of, claim 1 in which the solidifiable component of thedaylight fluorescent composition includes a vehicle of thermoplasticmaterial having a melting.

point above room temperature and below temperature destructive to thefluoragent, and including the steps of heating the daylight fluorescentcomposition to a molten condition below the temperature destructive tothe fiuoragent, applying the molten composition to the printing plate insubstantially the same thickness as the composition is to be applied tothe receiving structure, applying the composition to the receivingstructure in a tacky condition and in a single impress, and cooling thecomposition to room temperature after application to the receivingstructure.

13. The method of claim 1 in which the solidifiable component of thedaylight fluorescent composition includes a plastisol vehicle andincluding the steps of applying the composition to the printing plate insubstantially the same. thickness as the composition is to be applied tothe. receiving structure, applying the composition from the printingplate-to the receiving structure in a single impress, heating thecomposition on the receivingstructure to kick-over the plastisol to agel and then cooling the gel to room temperature.

14. The method of claim 1 in which the solidifiable component of thedaylight fluorescent compositionincludes a vehicle comprised of asolution of an anhydrous hygroscopic solvent in a resin insoluble inaqueous solution of the solvent, applying the composition to theprinting plate in substantially the same thickness as the composition isto be applied to the receiving structure, applying the composition tothe receiving structure in a single impress, and subjectng thecomposition to Water vapor to remove the hygroscopic solvent and depositthe solidifiable component on the receiving structure.

References Cited in the file of this patent UNITED STATES PATENTS1,928,758 Mairson et al. Oct. 3, 1933 2,147,651 Jones et al Feb. 21,1939 2,152,856 Switzer Apr. 4, 1939 (Other references on following page)13 UNITED STATES PATENTS Boente Oct. 22, 1940 Cornwell Dec. 31, 1940Erickson et a1 June 3, 1941 Jenkins Aug. 26, 1941 Huber Jan. 6, 1942Switzer et a1 Mar. 24, 1942 King Aug. 11, 1942 Switzer Nov. 17, 1942Huber June 22, 1943 Reese May 1, 1945 14 v Jones May 8, 1945 JenkinsJune 26, 1945 Chavannes Oct. 25, 1949 Chavannes Oct. 25, 1949 SwitzerFeb. 21, 1950 Switzer Feb. 21, 1950 OTHER REFERENCES available in Div.50.)

1. THE METHOD OF PRINTING DAYLIGHT FLUORESCENT MEDIA COMPRISING THESTEPS OF APPLYING TO A MECHANICAL PRINTING PLATE A RELATIVELY FLUID ANDTACKY DAYLIGHT FLUORESCENT COMPOSITION COMPRISED OF A DISPERSED SOLVATEDDAYLIGHT FLUORESCENT FLUORAGENT AND A VEHICLE CONTAINING A NON-VOLATILE,TRANSPARENT, RELATIVELY SOLIDIFIABLE COMPONENT, THE PROPORTION OF SAIDFLUORAGENT TO SAID SOLIDIFIABLE COMPONENT NOT EXCEEDING THE MAXIMUMCONCENTRATION AT WHICH SAID FLUORAGENT WILL EXHIBIT DAYLIGHTFLUORESCENCE; DEPOSITING FROM SAID PLATE ONTO A DELINEATED AREA OF ARECEIVING STRUCTURE IN A SUBSTANTIALLY UNIFORM THICKNESS, A VOLUME OFSAID COMPOSITION PROVIDING AN AMOUNT OF FLUORAGENT PER UNIT OF AREABETWEEN THE MAXIMUM AND MINIMUM REQUIRED TO EXHIBIT DAYLIGHTFLUORESCENCE OF FULL CHROMA AND PURITY OF HUE; SOLIDIFYING SAIDCOMPONENT TO A RELATIVELY NON-TACKY CONDITION WHILE RETAINING THEREINSAID FLUORAGENT IN A DAYLIGHT FLUORESCENT STATE; AND REMOVING THEPORTION, IF ANY, OF SAID RELATIVELY FLUID COMPOSITION NOT RETAINED INSAID SOLIDIFIED COMPONENT.